Urban Gray Matter Needs Trees

Noise, crowding and pollution all stress city dwellers' brains. But when there's a forest or park nearby, things change.

People who live in cities have to contend with noise and pollution in a crowded environment — all of which can cause chronic stress. So it is no surprise, given the beating their brains take, that city dwellers are at a higher risk for depression, anxiety and other mental disorders than country dwellers.

The stress of city living shows up in residents' amygdalas, a brain area that plays an important role in processing stress and reactions to danger. Spending time in nature, among trees, helps this brain area recover and cope, a German study has found.

By 2050, almost 70 percent of the world's population is expected to be living in cities.

When city dwellers are easily able to spend time among trees and greenery, their gray matter suffers less stress, researchers at the Max Planck Institute for Human Development in Germany found.

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“Research on brain plasticity supports the assumption that the environment can shape brain structure and function. That is why we are interested in the environmental conditions that may have positive effects on brain development. Studies of people in the countryside have already shown that living close to nature is good for their mental health and well-being. We therefore decided to examine city dwellers,” explained the study's first author, Simone Kühn.

The study involved almost 350 people, aged 61 to 82 years, who were part of the Berlin Aging Study. Researchers mapped where participants lived, using a map that showed forests, urban parks, bodies of water and wasteland. They matched the seniors' home environment to the men's and women's performance on a variety of cognitive tests. Participants were MRI scanned to assess the quality of brain activity from three brain areas, including the amygdala.

The researchers found that people who lived close to nature were more likely to show indications of a physiologically healthy amygdala structure and were therefore presumably better able to cope with stress.

Brain function was best preserved among those who lived within a 1 km radius of a natural area, a little more than .6 of a mile, who tended to retain their brain function best in the face of stress. Such a modest distance, the researchers suspect, made it possible for even older adults to gain the benefits of being in nature.

The study could not prove that exposure to trees and nature caused this improvement in the brain, but the association was significant; and as the distance from nature grew, amygdala function deteriorated. The observed association between the brain and closeness to forests will need to be confirmed in further studies and other cities, however.

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By 2050, almost 70 percent of the world's population is expected to be living in cities, according to Ulman Lindenberger, Director of the Center for Lifespan Psychology at the Max Planck Institute. The researchers hope the results will be used to inform urban planning in Europe and North America.